Description of the Related Art
Well known technology for developing electrostatic latent images formed on an image holder in a developing apparatus, such as an electrophotographic copying machine, is based on the utilization of a non-magnetic or magnetic single component developer (toner). The ability to control the layer thickness of the developer during the development process is crucial to this technology.
An example of developer thickness control technology is where a layer thickness control member contacts a rotating developer holder in the developing apparatus, so that the developer on the developer holder forms a uniform charged thin film necessary for the developing process. The electric charge is provided by frictional electrification. This thin developer layer is then transferred to a developing position where the image holder contacts the developer holder. As a result, the developer is supplied to the electrostatic latent image formed on the image holder, so that the latent image is developed.
One of electrophotography's foremost technical problems arises from the accumulation of excess developer around both ends of the developer holder, which faces the non-image areas of the image holder. The accumulation of excess developer is due to scattering caused by the rotation of the developer holder, so that the developer migrates to both ends of the developer holder virtually parallel to the longitudinal direction of the developer holder. The result is a surplus supply of the developer, causing the developer to scatter in the apparatus. This scattering of developer then causes contamination problems in the copying machine and results in unnecessary excess consumption of the developer.
A technology for preventing developer wastage and for protecting the developing apparatus from contamination is disclosed in the official report of Unexamined Published Japanese Patent Application No. 4-62391. The developing apparatus disclosed in the official report, shown in FIG. 26 and 27, is provided with an elastic plate-like layer thickness control member 101, a cylindrical developer holder 103, and elastic sealing members 102 covering both side edges 101a of the layer thickness control member 101 from the back side of the leading edge 101b. The elastic sealing members 102 cover portions on the face of the developer holder 103, which are close to both side edges 101a of the layer thickness control member 101. Consequently, the movement of the developer to both ends of the developer holder 103 in an axial direction parallel to a rotary shaft line of the developer holder 103 is restricted.
When the elastic sealing members 102 cover both side edges 101a of the layer thickness control member 101 and the face of the developer holder 103 around those side edges 101a as described above, to restrict the movement of the developer in the axial line direction, both side edges 101a of the layer thickness control member 101 are pressed directly against the face of the developer holder 101. If the developing apparatus is consistently used in this configuration, local damage occurs at a contact portion between the developer holder 103 and both side edges 101a of the layer thickness control member 101. This damage generates a gap between the developer holder i03 and the side edges 101a, resulting in degradation of the performance of the elastic sealing members 102.
Consequently, the movement of developer to both side edges of the developer holder 103 cannot be completely restricted, causing a surplus supply and scattering of the developer to both edges 101a and resulting in problems such as contamination in the developing apparatus and unnecessary consumption of the developer. This effect is exacerbated when the layer thickness control member 101 and the developer holder 103 are composed of different materials, each of which has mechanical characteristics significantly different from each other. For example, when the layer thickness control member 101 is composed of a plate-like metallic material and the developer holder 103 is composed of a roller-like rubber material, such the symptoms appear more markedly.
An additional prior art example is shown in FIG. 27. The edges 101c at both sides 101a of the layer thickness control member 101 contact the elastic sealing members 102 in the axial line direction. A problem arises from this contact as follows: each of the elastic sealing members 102 is stepped and the toner leaks from the gap S generated from this stepped portion and migrates to both ends of the developer holder 103.
Japanese Unexamined Patent Publication JP-A 4-249273 (1992) discloses a technology for eliminating such a stepped portion. FIG. 28 shows a layer thickness control member 111 held in place by dividing each sealing member 112 into a sealing member 112a used for the developer holder 113 and a sealing member 112b used for the layer thickness control member 111.
When the sealing members 112a and 112b are composed of different materials, the structure of sealing member 112 is complicated. In addition, since the sealing members 112a and 112b are bonded unitarily, problems will arise when the developer leaks from the bonded section, which results if the sealing property of the bonded section is low. Furthermore, two types of sealing members are needed for proper sealing. Therefore, another problem, an increase of the manufacturing cost, arises.
Referring to FIG. 26, both side edges 101a of the layer thickness control member 101 are restricted by the elastic sealing members 102 in the developing apparatus disclosed in Japanese Unexamined Patent Publication JP-A 4-62391 (1992). As a result, the pressure applied to both side edges 101a of the layer thickness control member 101 differs from the pressure applied to other portions. Consequently, a layer of developer is not uniformly formed on the developer holder 103, so the copying machine forms images having an uneven density of developer.
Furthermore, Japanese Unexamined Patent Publications JP-A 3-109587 (1991) and 2-287471 (1990) disclose technologies for restricting the movement of the developer in every direction other than in the one expected for feeding the developer in the developing apparatus having the configuration described above. The developing apparatus disclosed in JP-A 3-109587 forms sealing members for restricting the movement of the developer to the one expected for feeding the developer by using bristle set sealing members, each of which is composed of many types of materials. The developing apparatus disclosed in JP-A 2-287471(1990) is provided with a sheet for preventing developer leakage from a developing tank, which sheet is in contact with the outer peripheral surface of the developer holder in the developing tank, and the pressure with which the sheet is in contact with the outer peripheral surface is higher at the end portions of the sheet than in the center portion.
Japanese Unexamined Patent Publication JP-A 4-115271 (1992) discloses prior art for preventing the developer holder or the layer thickness control member from damage in the developing apparatus described above. In the case of the layer thickness control member, the width of the layer thickness control member in the direction parallel to the rotary shaft of the developer holder is wider than the width of the developer holder.
When any of the developing apparatuses and the developing units in the three official reports described above are used, it is difficult to prevent the developer holder and the layer thickness control member from becoming damaged. As a result, the prior art is unable to restrict the movement of the developer to the one desired for feeding the developer.